Britain's continued membership in the European Union is contingent upon its being allowed to stop migrants from the bloc from tapping into its relatively generous welfare system, Prime Minister David Cameron will warn Friday.

In a speech designed to breathe new life into his campaign to be re-elected in May, Cameron will say he wants employed EU migrants to have to wait four years before they can access welfare benefits and for unemployed EU migrants not to be eligible for any help from the British state at all.

With polls showing immigration is voters' top concern, Cameron is under pressure to take a tougher line on the issue. Many of his fellow Conservative lawmakers fear the rise in popularity of the anti-EU UK Independence Party, which this month won its second seat in Parliament, threatens their re-election chances.

Polish objections

The speech is likely to upset EU partners such as Poland, which has suggested such measures would be discriminatory. But Cameron will not call the EU's freedom-of-movement rules into question as some EU leaders had feared and will not advocate migrant quotas or an "emergency brake" on inflows.

The freedom-of-movement rules entitle EU citizens to work anywhere in the bloc.

If re-elected, he has promised to renegotiate Britain's ties with the EU before giving Britons an in/out membership referendum in 2017.

Cameron will make it clear Friday that he thinks his renegotiation will succeed. But he will also drop his strongest hint yet that he may campaign for Britain to leave the bloc if he fails.

"I will negotiate a cut to EU migration and make welfare reform an absolute requirement in renegotiation," Cameron will say, according to advance extracts released by his office.

"If I succeed, I will, as I have said, campaign to keep this country in a reformed EU. If our concerns fall on deaf ears and we cannot put our relationship with the EU on a better footing, then of course I rule nothing out."

300,000 would be affected

If implemented, his proposals would affect over 300,000 EU migrants, many of them working in low-wage, low-skilled jobs.

Welfare payments to EU migrants' children living outside Britain would be stopped, and jobless EU migrants would be removed if they were unable to find work within six months.

Nationals from member states joining the EU in the future would also be banned from joining the British labor market until their home economies had converged more closely with those of current members.